Method of making stencils



July 27, 1954 A L RQ5HK|ND ET AL 2,684,628

METHOD OF MAKING STENCILS Filed Jan. 5, 1951 ,459, j f; 2%22 ff /3 STENCLIZABLE SHEET \INK OR CARBON SHEET /NVENTORSI 4 Mrz ayv Mm m Arron/vers.

Patented July 27, 1954 UNITED STATES ATENT OFFICE METHOD OF MAKING STENCILSy Application January 5, 1951, Serial No. 204,608

9 Claims. l

This invention relates to stencils, and materials and methods for manufacturing the same, and it relates more particularly to the manufacture of stencils for use in duplicating work.

In a copending application Ser. No. 165,490, led on June l, 1950, by Allan I. Roshkind, now abandoned, description is made of a concept employing a heat pattern generated by an original subjected to radiant energy for dissipating or otherwise rearranging an ink impervious composition which coats or impregnates a stencil base tissue to provide openings corresponding to the letter outlines of the copy through which ink may pass in normal duplicating processes. In

another copending application Ser. No. 178,220,

led on August 11, 1950, by Keith S. Hoover, description is made of the use of a heat pattern generated by radiant energy absorption in an original or letter outline positioned onto or adjacent a plastic lm to cause rearrangement oi the heated portion of the plastic film into openings corresponding to the letter outlines and through which ink may pass to form a new and improved unsupported stencil suitable for use in normal stencil duplicating processes.

It has now been found that a stencil suitable for use in the preparation of a large number of copies by normal stencil duplicating techniques may be fabricated Without the use of a resinous or plastic material and without the use of an ink impervious composition coating or impregnating a porous stencil base tissue. In accordance with this invention, a stencilizable sheet is formed of a novel mixture of fibers, which will hereinafter be described, the sheet being calendered, iilled or otherwise treated, to resist the passage of ink under conditions of use in stencil duplicating processes. A heat pattern generated by the phenomenon of radiant energy absorption in the desired letter outlines functions in the heated areas of the stencilizable sheet to eliminate by disintegration, through burning out or the like, a large proportion of the bers of which the ink impervious stencil sheet is formed to leave letter openings through which ink may pass. In order to maintain the position of the loop letters and in order to provide a network of connecting iibers across the openings left by the disintegrated, burned out or removed fibers, the stencilizable sheet is formed with a quantity of heat insensitive fibers mixed with heat destructible fibers such that the heat insensitive fibers remain in their original position in the formed stencil sheet to tie in the loop letters with the body of a sheet and to provide a fibrous network or Vweb across the opening,

(Cl. 10b-128.4)

It is an object of this invention to produce a stencilizable sheet of the type described and it is a related object to produce a stencil and to provide a method for producing the same from said stencilizable sheet.

It is another object to produce a stencilizable sheet of the type described and to `provide a method to produce a stencil therefrom by the use of heat patterns generated from an original by the phenomenon of radiant energy absorption and it is a related object to produce a stencilizable sheet which may be used in the manufacture of a stencil from copy arranged adjacent thereto or from letter outlines applied directly onto the surface of the sheet.

These and other objects and advantages of this invention will hereinafter appear, and for purposes of illustration, but not of limitation, embodiments of the invention are shown in the accompanying drawing, in which Figure 1 is a top plan view of a stencilizable sheet embodying features of this invention;

Figure 2 is a sectional elevational view illustrating the use of a stencilizable sheet in the preparation of a stencil from copy positioned in surface contact therewith;

Figure 3 is a sectional elevational View corresponding to that of Figure 2 indicating the reactions which occur upon exposure of the assembly to radiant energy;

Figure 4 is a top plan View of a stencil sheet formed by the elements and steps shown in Figures 1, 2 and 3;

Figure 5 is a schematic elevational View showing a stencilizable sheet in position for applying letter outlines directly thereto;

Figure 6 is a top plan view of the stencilizable sheet processed in accordance with Figure 5, and

Figure 7 is a top plan View of the sheet shown in Figure 6 after exposure to radiant energy.

In the practice of this invention a stencilizable sheet l0 formed of heat destructible or disposable bers H in admixture with a small proportion of heat insensitive'fibers I2 is arranged substantially in surface contact with letter outlines or copy desired to be reproduced by the stencil by normal stencil duplicating technique. Radiations rich in infra red are directed onto the copy whereby radiations are absorbed by inaterial in the copy and converted into heat to form a heat pattern corresponding to the copy. The heat pattern is transmitted to the stencilizable sheet and causes substantial elimination by burning out, decomposition or the like of the destructible fibers that are raised to elevated temperatures, leaving the heat insensitive iibers I2 as a network or web across the openings that are formed and through which ink is able to pass in normal stencil duplicating operations.

It is preferred to fabricate the stencilizable sheet with kraft or a sulphite type pulp cellulosic fibers as the disposable or destructible fibers and with mineral fibers, such as glass, asbestos and rock wool and the like, as the heat insensitive fibers. In the event that the heat insensitive fibers are selected of such inorganic mineral bers, other natural fibers such as wool, cotton, silk, hemp or the like, or synthetic resinous bers such as polyamides (nylon), vinyl acetate-vinyl chloride (Vinyon), cellulose acetate (rayon), polyvinylidine chloride (Saran), regenerated cellulose and the like may be used alone or in admixture with the cellulosic type pulp fibers. In the event that the heat destructible fibers are of the cellulosic type which are destructble at relatively low temperature, the heat insensitive bers may be formed of materials having higher softening point and greater inertness to heat which includes synthetic bers, such as Saran, rayon, nylon and the like.

It is preferred to use stencilizable sheet stock in which bers are present in the ratio of about 20 parts by weight heat insensitive nbers to about 80 parts by weight heat destructible fibers, but in any event it is best if the ber ratio is maintained in excess of 60 percent by weight heat destructible fibers and more than 3 percent but less than 40 percent by Weight heat insensitive fibers. When more of the latter is used, the amount of fiber which remains in the stencil openings that are formed tends to obstruct the desired ilow of stencil duplicating ink required for successful high speed stencil duplicating operations.

The stencilizable sheet may be formulated with fillers, such as finely divided silica, diatomaceous earth, celite, titanium dioxide, chalk and the like to bulk up the sheet stock and to improve the resistance of the formed sheet stock to the passage of ink composition. It is best if the stencilizable sheet stock is calendered or compacted to increase its resistance to the passage of ink except through formed stencil openings. Such highly calendered sheet stock, particularly when formed of highly pulped fibers, tends to form a continuous film having the characteristics of glassine paper and the like which is highly resistant to the passage of ink. Highly calendered sheet stock having a thickness of about 0.002 and formed of pulp bers and glass wool fibers which are about 1/8 inch in length has been used successfully in the manufacture of stencilizable sheets wherein the glass fibers are present in the concentration of about percent by Weight of the finished sheet. Glass fiber lengths ranging from 1/16 to 1/2 inch and more have also been successfully used.

The copy from which the stencil sheet is prepared may be in the form of an original adapted to be placed in surface contact with the stencilizable sheet, as shown in Figure 2. Upon directing radiations onto the copy as by flashing a photographers lamp or the like, the radiations are reflected or otherwise dissipated by the white background and absorbed and converted into heat by material in the lett-er outlines or dark areas of the copy. The heat transfers as a pattern corresponding to the letter outline to the stencilizable sheet whereupon the heat destructible bers are eliminated in areas corresponding to the heat pattern or letter outlines, leaving the heat insensitive fibers as a highly porous matrix or web which anchors the loop letters in place and provides a desirable lattice-work through which ink composition may be caused to flow in normal stencil duplicating work.

Instead of using an original from which a stencil is to be formed, the letters or outlines to be duplicated may be applied by means of a carbon, typing ribbon, pencil or other Writing instrument directly onto the surface of the stencilizable sheet, as shown in Figure 5. Upon radiation of the stencilizable sheet, the radiant energy is dissipated by the uncolored or unmarked areas of the sheet and absorbed by material in the letter outlines and converted into heat. The heat formed almost immediately causes removal of the heat destructible fibers leaving the heat insensitive bers as an interconnecting web across the formed stencil opening vacated by the heat destructible fibers and through which ink may pass. When making use of a carbon to apply the letter outlines directly onto the stencilizable sheet, excellent results are secured when the carbon is arranged between the sheet and platen so as to apply the carbon coating on the reverse side of the stencilizable sheet.

An important concept of this invention resides in the use of an activator for causing destruction and removal of the heat destructible bers to occur at lower temperatures which preferably should be above room temperature in the event that the stencilizable sheet is to be marketed With such activating agent as a part thereof. Such degradating or catalytic agents, particularly adapted for use with cellulosic pulp fibers, may be selected of inorganic acids and acid salts, such as hydrochloric acid, sulfuric acid, aluminum chloride, bismuth chloride, ferrie chloride, cupric chloride, stannic chloride and their corresponding sulphates, bisulp'hates and persulphates, such as cupric sulphate, ferrous ammonium sulphate, chromium sulphate, potassium sulphate, potassim bisulphate, mercurio sulphate, and ammonium persulphates, peroxides, perchlorates, nitrates and the like oxidizing agents. rl'hey may also be selected of organic acids and acidic compounds, such as citric acid, aniline hydrochloride, aniline nitrate1 aniline bromide, aniline hydrobromide, organic sulfonic acid, l-naphthalene, li-sulfonic acid and other organic acids, such as indophenol, ammonium thiocyanide, coupled with ferric chloride and the like and mixtures of such compounds. These activating agents may be incorporated directly into the stencilizable sheet as a coincident with the deposition of the nbers during sheet formation or they may be incorporated before or afterwards as by coating or impregnation. They may be incorporated into the ink composition applied directly to the stencilizable sheet or they may constitute an ingredient of the carbon coating which is transferred onto the surface of the stencilizable sheet in accordance with the practice of this invention. In the use of such activating agents, it is preferred to embody such materials into compositions that are applied onto the surface of the stencilizable sheet so as to catalyze only those portions of the fibers which are adapted to be removed upon exposure to elevated temperature.

The concentration of the activating or catalytic agent is unimportant so long as it is able to lower 'the temperature by which the fibers are destroyed and accelerate their destruction so that complete elimination may be effected in minimum time.

Usually concentrations ranging from 0.1 to percent by weight based upon the fibers to be destroyed is suflicient.

Radiant energy capable of the phenomenon of heat generation upon absorption in material comprising the letter outlines associated with or applied directly to the surface of the stencilizable sheet may be derived from light sources rich in infra red, which include rays having a wave length ranging from 8,000 to 40,000 angstroms. Radiant energy capable of the phenomenon described may be developed in sufliciently high concentration by an ordinary photographers fiash lamp and may be generated by a tungsten filament lamp, carbon aro lamp, infra red ray lamp and the like. The amount of heat developed depends greatly upon the duration of exposure and the intensity of the usable rays in the light beams. The amount of heat developed depends also upon the depth and the intensity of the color in the copy and the character of the material of which it is formed. It is possible in order to achieve higher heat concentration to embody converters in the form of dyes and other chemical compounds for making greater use of the radiant energy and converting those beyond the usable range into rays capable of absorption and heat generation for use in the practice of this invention.

In one system for practicing this invention, an

im: impervious calendered stencilizable sheet lil formed of 10 percent glass fibers I2, having a mean length of about 1A; inch, and about 90 percent kraft pulp bers II is arranged in surface contact with an original I3 with the letter outlines I4 uppermost.

Upon radiation of the assembly, as by flashing of a number 50 photographers lamp l5 above the surface of the original, as shown in Figure 3, radiations generated by the lamp are dissipated or otherwise reflected by the surface free of the letter outlines and absorbed by material in the letter Outlines ift and converted into heat. The heat shown by the broken lines I6 in the original (Figure 3) is transmitted directly to the stencilizable sheet it whereupon th-e pulp fibers are immediately burned out leaving the glass bers I2 in their original position as a web across the formed opening il through which ink may now pass. tions of the. stencilizable sheet and serve to anchor the loop letters lil and prevent their removal along with the destroyed pulp fibers.

Instead of employing a stencilizable sheet formed of cellulose and glass fibers, the sheet may be formed of about 10 percent polyvinylidine chloride (Saran fibers) felted in uniform distribution with cellulosic bers and having about .5 percent zinc chloride distributed therewith. The zinc chloride catalyzes the destruction of the pulp fibers so that their elimination can be effected at temperatures below 250 F. with the result that upon exposure of the original to radiant energy rich in infra red, the heat pattern that develops functions to eliminate the pulp fibers Without affecting the Saran fibers which are considered to be heat insensitive under conditions of use.

ln the modification shown in Figures 5 to 7, inclusive, a stencilizable sheet iii formed of abo-ut percent glass fibers and 80 percent pulp fibers impregnated with 1.0 percent ferrie chloride is arranged on a typewriter platen 2S with a carbon paper 2i disposed therebetween. The carbon paper embodies a composition containing ferric The glass fibers tie in the unaffected por- I sulphate inV relatively high concentration with a tinctorial agent of carbon black or the like. Upon impact with a typewriter key 22, the colored coating 23 of the carbon paper is transferred onto the inner surface of the stencilizable sheet i0, as shown in Figure 6, and upon radiation, as by a pencil point of light from a carbon arc lamp adapted slowly to` traverse the sheet, the radiations are reflected or otherwise dissipated by the untyped surface of the stencilizable sheet and absorbed by the applied letter outlines and converted into heat. The light source is passed over the stencilizabie sheet at a rate to develop suicient temperature, such as about 250 F., whereupon the heat destructible pulp fibers are removed leaving the glass fibers 24 as a web across the stencil openings 25 through which ink may pass. Instead of ferrie chloride, others alone or in combination of the degradating or catalytic agents previously described may be substituted in whole or in part.

It has been found that best definitionis secured when sufficient heat is developed by the absorbed radiations in a minimum amount of time. When prolonged exposure is employed to develop adequate heat to accomplish the desired fiber construction there is a tendency for the heat to migrate laterally from the heat pattern and consequently affect adjacent bers so as to produce excessively bold and ragged copy. In order to accomplish the desired instantaneous but concentrated exposure, it is preferred to use a photographers flash lamp, as shown in Figure 3, or devices in which the source of infra red ray-bearing light is energized at high wattage by a capacitor similar tol that which is used in industrial spot-welding. Another device which may be used to accomplish the desired short exposure to intense usable rays consists of a relatively long but thin source of infra red radiation, such as a hot Wire or tungsten filament lamp. A still further device for accomplishing the desired short but intense exposure consists of a point source of infra red ray radiation, such as an incandescent lamp in which the radiations are focused to a relatively fine point through a lens system onto the surface of the stencilizable sheet or copy. During operation the point source of light is moved at a constant rate in a direction parallel to the surface of the stencilizable sheet or copy until each point element of the letter outline has been exposed to the concentrated radiations.

It will be apparent from the description that We have provided a new and improved system for preparing masters and stencil sheets of per manent character on what appears to be ordinary white paper and in which the actual duplicating master can be obtained rapidly and eiciently upon exposure in a suitable radiation device. It will be apparent that a stencil sheet prepared in accordance with this invention constitutes an economical product available for manufacture and use with inexpensive equipment that can be made readily available and operated with little cost or skilled labor.

A stencilizable sheet prepared in accordance with this invention does not require special tissue no1' coating operations characteristic of present stencil manufacture practice. It permits stenci1- ization by normal typing procedures normally practiced in the preparation of copies on light bond paper and the preparation of stencils therefrom utilizes systems and apparatus which are convenient to handle and readily available to all.

It will be apparent from the description that this invention provides a basically new concept for preparing stencils which conform almost identically with an original copy or which conform exactly with letter outlines applied directly thereto, as by typing or stylus work. The technique described and claimed herein suggests itself for many other applications and for numerous variations with respect to materials and methods of handling and it will be understood that numerous changes may be made in the details oi construction, arrangement and composition without departing from the spirit of the invention, especially as defined in the following claims.

We claim:

l. The method of producing a stencil comprising the steps of arranging an ink impervious sheet formed of a felted layer of heat destructible fibers in admixture with a smaller proportion of heat insensitive fibers substantially in surface contact with letter outlines containing a material which is infra red ray absorbing and heat generating, directing a sufficient quantity oi radiations of infra red onto the letter outlines to generate a heat pattern which upon transfer to the impervious sheet causes destruction of the heat destructible bers leaving the heat insensitive fibers as an inter-connecting web across the openings that are left by the removed heat destructible bers and through which ink may pass in normal stencilling operations.

2. The method as claimed in claim 1 in which the heat destructible fibers comprise more than 60 percent by weight of the sheet and in which the heat insensitive fibers comprise less than 40 percent by weight of the sheet.

3. The method as claimed in claim 1 in which the heat destructible iibers comprise cellulose pulp bers and in which the heat insensitive bers comprise mineral fibers.

4. The method as claimed in claim 1 in which the sheet contains an activating agent which lowers the temperature at which the heat destructible bers are removed from the sheet.

5. The method of producing a stencil comprising the steps of applying letter outlines formed Vof a material which is infra red absorbing-heat generating directly upon a stencilizable sheet in the form of a felted layer of heat destructible fibers in admixture with a smaller proportion of heat insensitive fibers, directing a suiiicient quantity of radiations of infra red onto the letter outlines whereby the radiations are absorbed by the material in the letter outlines and converted into heat to form a heat pattern which upon transfer causes removal of the heat destructible iibers leaving the heat insensitive fibers as a web across the formed openings through which ink may pass in normal stencil duplicating operations.

6. kThe method as claimed in claim 5 in which the stencilizable sheet is formed of more than 60 percent by weight cellulosic pulp fibers and less than 40 percent by weight glass bers.

7. The method as claimed in claim 5 in which the applied composition forming the letter outlines contains a degradating agent which lowers the temperature at which the heat destructible bers are removed from the stencilizable sheet.

8. The method as claimed in claim 5 in which the letter outline is applied as by typing on the stencilizable sheet through a typewriter ribbon containing a color composition combined with a degradating agent which lowers the temperature at which the heat destructible nbers are removed upon exposure of the stencilizable sheet to radiant energy rich in infra red.

9. The method as claimed in claim '7 in which the letter outlines are applied by transfer of a carbon coating by force onto the surface of the stencilizable sheet.

References Cited in the iile oi this patent UNITED STATES PATENTS Number Name Date 215,833 Nickerson May 27, 1879 458,840 Andrews Sept. l, 1891 '789,153 Horn et al. May 9, 1905 1,494,667 Coe et al May 20, 19-24 1,518,944 Sulzberger Dec. 9, 1924 1,581,618 Sulzberger Apr. 20, 1926 2,309,440 Bur June 25, 1943 2,504,744 Sproull et al. Apr. 18, 1950 2,507,827 Stafford et al May 16, 1950 

